Although people living with HIV (PLWH) are increasingly linked and retained in HIV medical care, viral load suppression rates are not meeting benchmarks. Ryan White Part A (RWPA) ancillary service (e.g., food/ nutrition, housing, legal advocacy, substance abuse treatment) providers frequently have contact with ?floaters,? or PLWH who are not in RWPA services that offer HIV care and treatment adherence support (e.g., medical case management; MCM) and only access services to meet their basic needs. Ancillary service providers are an untapped opportunity for supporting HIV care and treatment adherence. From 3/2014 to 2/2015, 41% of New York City (NYC) RWPA clients were floaters. Of these, 36% were virally unsuppressed at some point during that year. Floaters comprise a large group of PLWH who need support in achieving VLS and are uniquely reachable through RWPA ancillary service providers. The goal of this mixed methods study is to use multiple data sources, including the NYC HIV Surveillance Registry (viral loads), Salient Information Manager (Medicaid information), Electronic System for HIV/AIDS Reporting and Evaluation (RWPA client data), and qualitative interviews to inform the development of feasible and acceptable HIV care and treatment adherence support interventions that could be delivered by ancillary service providers. A major strength of this study is our use of large NYC datasets to analyze service utilization and VLS in floaters. The Specific Aims are: (1) To use RWPA client, HIV surveillance and Medicaid data to better characterize floaters in terms of client and health care environment characteristics (e.g., agency and provider factors) and ancillary service utilization patterns, and to examine the association of these factors with viral load suppression; and (2) To use in-depth interviews with clients and providers, and questionnaires with RWPA program administrators to: (a) identify clients' perceived barriers to and facilitators of HIV care and treatment adherence and participation in MCM, and attitudes towards receiving HIV care and treatment support from ancillary service providers, (b) assess ancillary service providers' awareness of floaters, efforts to support their HIV care and treatment adherence, and willingness to do so; and (c) identify health care environment characteristics that would facilitate or inhibit the implementation of HIV care and treatment adherence support interventions delivered by ancillary services providers. Together with a Community Collaboration Board, we will use these data to develop interventions that will be further developed and testing in a subsequent R34 study.